An example of active gate control for changing the rate of discharging the gate of an insulated-gate transistor, such as an IGBT (Insulated-Gate Bipolar Transistor), within a period from the start of dissipating charge stored in the gate to completion of the dissipation is known in, for example, Japanese Patent Publication No. 3373704, referred to as a first patent document. The known active gate control requires a differentiating circuit for outputting a signal indicative of a derivative value of a collector current flowing through an insulated-gate transistor. The known active gate control changes the discharge path connected to the gate of the insulated-gate transistor from a low-resistance discharge path to a high-resistance discharge path based on a result of comparison between the level of an output signal from the differentiating circuit and that of a reference signal. Specifically, the known active gate control is designed to increase the resistance of the discharge path connected to the gate of the insulated-gate transistor if the rate of reduction of the collector current is equal to or higher than a predetermined value. The known active gate control reduces an increase of a surge produced based on the rate of reduction of the collector current while reducing switching loss.
Another example of the active gate control is known in, for example, Japanese Patent Publication No. 3339311, referred to a second patent document. The active gate control known in the second patent document provides a driver for a voltage-controlled switching element, such as an IGBT; the driver includes two discharge paths connected to the voltage-controlled switching element and having different resistance values. The active gate control known in the second patent document achieves the same effect as that known in the first patent document.